The invention is related to a screw actuator, comprising a screw and a nut which are each provided with at least a helical groove, and a series of rollers or balls which are in rolling contact with said grooves.
Such actuator is generally known. The internal actuator space defined between the nut or screw is usually protected with respect to the outside by means of seals or shields. Further properties of the actuator are related to the way in which the balls are circulated, e.g. by means of inserts protruding into the groove windings, or by means of a circulation tube.
These components, i.e. seals, shields, inserts and tubes, all contribute considerably to the manufacturing costs of the actuator. It is therefore desirable to streamline the actuator production in this respect, so as to obtain reduced production costs. To that end, the actuator according to the invention is characterized by a multi-purpose sleeve which surrounds the nut at least partly, which sleeve plays a role in mounting said components. Said sleeve may even constitute said components.
For instance, the sleeve may carry a shield or seal which acts between the nut and screw. Such sleeve and seals or shields may be pre-assembled, and may be fixedly connected to the nut.
Preferably, the seal is a wiper seal. Alternatively, the sleeve functions as a carrier for a separate seal ring having the same helical groove as the rest of the nut. Said seal ring may be made of a non-metallic material with or without impregnated lubricant.
The sleeve may protrude with respect to the nut, the protruding end of the sleeve carrying the seal, or a shield.
In case the nut is provided with a support bearing, said sleeve may carry a second seal for sealing the bearing space of said bearing.
According to one of several possible embodiments, the nut of the screw actuator may comprise at least one radially oriented through-going aperture which accommodates an insert for moving the balls between axially adjacent parts of the groove. According to the invention, the sleeve retains said insert within said aperture.
Alternatively, the nut may comprise a bypass for moving the balls between the opposite ends of a multiple of windings of the grooves, wherein the sleeve at least partially defines said bypass. In particular, the sleeve may comprise a protrusion which delimits the radially outer part of a bypass tube.
Furthermore, the inner ring of the bearing may be integrated with the nut. In the screw actuator according to the invention, said bearing is an asymmetric angular contact bearing, the outer ring of which has a low shoulder at the side near the sleeve, said sleeve extending into the gap defined by said low shoulder of the outer ring and the opposite shoulder of the inner ring, the second seal engaging the inner surface of said low shoulder.
Additionally, means may be integrated in the actuator for replenishing the lubricant for the grooves and rollers or balls of the actuator. The grooves may have a somewhat deeper, through-like bottom for accommodating some grease, and the replenishing means open out in said grooves or through-like bottoms.
The invention is also related to a brake calliper comprising a screw provided with a bore, and a nut which are each provided with at least a helical groove, and a series of rollers or balls which are in rolling contact with said grooves.
According to the invention, a sleeve is provided which covers the wall of the screw bore at least partly.
The nut at one end may be closed by means of an end cap. The enclosed space may contain an amount of lubricant for lubricating the grooves of the actuator via suitable apertures, e.g. by bleeding the oil from an amount of grease. Alternatively, active pump means may be provided for expelling the grease into the grooves.
In this respect, the actuator may be sealed for life by means of said end cap, a lubricant being available in the sealed space.
The end cap may also fulfil further functions, and may for instance carry means for connection to a drive source.
The brake calliper according to the invention may comprise more than one actuator, e.g. two or four, each engaging a brake pad. Moreover, one of the nut and screw is supported rotatably with respect to the housing by means of a rolling element bearing. Preferably, each screw is connected to a piston which is slidably but non-rotatably held within a cylinder space in the housing, the nut being supported with respect to the housing by means of the rolling element bearing.
The sleeve carries a shield or a seal which acts between the nut and screw; said shield or seal is fixedly connected to the nut, and may frictionally engage the screw. The seal may be a wiper seal.
Furthermore, the sleeve may carry a sensor for sensing relative movements between the screw and the nut, e.g. relative rotation and/or translations.
The invention is furthermore related to an alternative embodiment of the brake calliper, which differs from the brake calliper described before in that the screw has a bore, and in that a sleeve is provided which covers the wall of the screw bore at least partly.
In particular, the screw may now be provided with at least one radially oriented through-going aperture comprising an insert for moving the balls between axially adjacent parts of the grooves, wherein the sleeve retains said insert within said aperture.
In this case, the screw is provided with a support bearing, the outer ring of the support bearing being integrated in the screw. The inner ring is accommodated within the screw bore. Furthermore, the sleeve may be prolonged by means of a small diameter tube part which extends through the inner ring of the bearing. Said tube part may be used for transferring a drive action onto the screw.